Cannabis use reduces thalamic volume in people at risk of schizophrenia

Embargoed until 01 November 2011

Using cannabis can lead to a loss of brain volume in people who are
at risk of developing schizophrenia, according to a
study published in the November issue of the British
Journal of Psychiatry.

The finding by researchers from the University
of Edinburgh could be important in understanding more fully the
link between cannabis use and the development of schizophrenia.

Previous studies have found that the brains of
people with schizophrenia show structural abnormalities,
particularly in a part of the brain called the thalamus. We each
have two thalami – the left and the right – which are responsible
for processing and relaying information.

The team studied 57 people aged between 16 and
25 who were well but who had a strong family history of
schizophrenia – and were therefore at high genetic risk of the
disease. Each person had a full assessment including a magnetic
resonance imaging (MRI) scan. Two years later, each person returned
for another MRI scan. As part of this second assessment, they were
asked about their use of illicit drugs (including cannabis),
alcohol and tobacco in the period between scans.

Of the 57 participants, 25 had used cannabis
between the two assessments. The researchers found that those
people who had used cannabis experienced a reduction in their
thalamic volume. This loss was significant on the left side of the
thalamus and highly significant on the right. No volume loss was
found in those who had remained cannabis-free during the two-year
period.

Some of the participants who used cannabis had
also used other drugs, such as ecstasy and amphetamines. However,
the results remained significant after controlling for this.

Lead researcher Dr Killian Welch said: “Our
study demonstrates that cannabis use by people with a family
history of schizophrenia is associated with thalamic volume loss.
This raises the possibility that when used by people already at
elevated genetic risk of the condition, cannabis may increase the
likelihood of brain abnormalities associated with schizophrenia
developing. This may facilitate our understanding of how cannabis
use can lead to a worsening of previously subtle symptoms – and
ultimately increase the risk of transition to schizophrenia.”